The present invention relates to devices for the monitoring of tires. More particularly, it relates to the transmission of the pressure and temperature of the tire to the chassis of the vehicle without galvanic contact.
The state of the art contains numerous attempts directed at advising the driver of a vehicle of a decrease in the pressure of one of his tires. U.S. Pat. No. 4,389,884 proposes that the detection be effected by means of bellows which move a ferrite within a coil in order to modify the value of the inductance thereof as a function of the pressure. The transmission is effected by inductive coupling between two coils, one fastened to the rim and the other to a part of the vehicle which is not movable in rotation. European Pat. No. 45,401 contemplates feeding an active circuit arranged in the tire with energy, modulating an electric signal in frequency as a function of the pressure, transmitting the signal towards the chassis by inductive coupling, and analyzing this signal as a function of various parameters. Among the various arrangements which independently monitor two or more variables within the tire, mention may be made of U.S. Pat. No. 4,052,696 which describes an arrangement which gives a warning when a pressure threshold or temperature threshold is exceeded.
The known devices have proven unable to assure reliable and precise monitoring of the condition of a tire. The behavior of a tire is, as a matter of fact, very complicated and the monitoring thereof cannot be reduced to the simple detection of a threshold. It is desirable to know continuously the pressure and the temperature prevailing within the tire. As already stated, it is not sufficient to transmit a threshold-exceeding signal of the parameters considered; it is necessary for a monitoring device to be able to transmit a measurement of said parameters, the measurements transmitted being capable of use for direct reading or being processed by an analysis system which controls a warning unit located on the instrument panel.